Tuesday, February 5, 2019

Sig Cub Electric Free Flight

For me there is something fun and challenging about trying to push something of lower performance to perform at close to an optimum level. The people that build and race the full-scale solar cell powered cars would be a good example of this. My challenge has been to build and fly an electric powered free flight model using the STRIX motor timer, 7 mm coreless electric motor, and one cell lipo battery of around 200 mah.

Sig Cub Electric 

Constraints of the timer dictate a motor run time of 10 seconds or less, and the size of motor and battery are limited also. I have personally limited myself to not using a gear drive. The weight of the electrical components is around 12 grams, if I remember correctly. From my experiments with adding the electrical system to various rubber models I believe optimum wingspan is about 22” to 24”. The most recent plane that I constructed just for this electric system is the Sig Cub. Several years ago I had built a Sig Cub for the intended rubber power and lost it to a thermal with just hand winds.

Flying at 23 Degrees F Motor would cut out

To cut the weight and the drag down further of electric system I left off the landing gear and cut the height of the pylon down. For the wing I used 3 mil mylar and then tissue just on the bottom for some color. The tail surfaces are covered with Esaki tissue and sprayed with an art spray which someone suggested might help the warping problem. It has not worked well and at the right conditions the stab starts to look like a potato chip. I did not pre-shrink tissue, but I think some type of plastic will be used to replace the tissue on the tail.

Launched Too Steep

Beyond the specifications of the airplane, I try to improve the flight by constantly tweaking what I can easily adjust on the airplane. That is position of the wing, rudder trim tab, and angle of launch. To get a longer flight you want it to climb as steep as possible without stalling and the plane transitioning from power to glide as close to level as possible. With this rather weak power package a real steep climb results in bad stalling and a very short flight. Other times I notice the plane climbing and diving in a very gentle manner. No doubt it is stalling but by a smaller amount. The best flights are in a constant climb angle with no hint of a stall with a fairly large turn radius because too tight a spiral wastes energy also.

This Looks to be Good Altitude for this Power System

Straight Pins Used on Rudder Trim Tab

What I like about electric is it is possible to get a large number of flights in because time is not needed to wind a rubber motor or fill an engine with fuel. Batteries need to be swapped out fairly quickly however because performance goes down with multiple runs. What I like about this weak electric flight is the plane is relatively close in and easier to observe.  A negative I have found is that the electric system does not work well below 30 degrees F, but then that is not great flying weather either.

Bill Kuhl

Related Links

https://sigmfg.com/products/sigff1-sig-cub-kit  Sig Cub on Sig Website



In the video the climb is not consistent all the way up and duration is not as good as it could be. Probably turning a little tight also.

Tuesday, January 8, 2019

Adventure with Green Hornet Electric Starter

Now that I keep acquiring more ½ A glow engines to power free flight and control line model airplanes, I decided an investment in a ½ A glow starter might be wise. Besides the starter I ordered a couple of new glow clips that are like a clothespin and some metal tanks for control line from Brodak. Last evening I was anxious to try the starter out on an AME .049 that had only been run once before. This time I used a Red Cap bladder cut in half because I did not need the larger capacity.

AME .049 Did not Run Well on Suction Feed

First thing I notice was the Hornet starter turns the .049 engine over really fast. Pushing it into the prop nut the prop came lose sending the nut, shaft, and propeller shooting across my messy basement. Luckily I found everything, this time I really tightened it. Yet it kept coming loose. Now I think it had something to do with the fit of the drive washer. After many times of tightening it stayed tight.

Starter Cone on Hornet 1/2 A Starter

As I had found out from questions after the first time running this engine, it does need to run on pressure. I did not want to run it for long as this was in my basement but I could tell that it was not having trouble with fuel suction as it did without pressure. I did not put a tach on it but it sounded like it was turning up pretty good. This is with a Cox 5x3 propeller; I have on order the APC props that people recommend for this engine. The new glow clip worked much better than using a Cox clip.

Bolt Ran into an Obstruction

After some frustration I was pretty happy that I will be able to start and run this engine without much trouble. As I put stuff away I noticed the aluminum cone on the starter was loose, there was a hole for a set screw but I could not see anything in it. I found a bolt that fit the hole and the threads matched perfectly. It would turn easily but about ¼” in it would stop; now I am worried I broke off a screw inside. Then it dawned on me that the set screw might use an allen wrench to tighten. Sure enough I found the correct size and was able to loosen the set screw and re-tighten the aluminum cone. 

Bringing the Set Screw Out

It appears to me that having the acorn nut used with an electric starter come loose is more of an issue than when I flew glow RC using a plastic spinner years ago. I am afraid if I tighten too tight something could break or strip out. The only prop nut I had for my Witch Hawk 500 came off at the Nats and luckily I found it in the grass. Any suggestions on this are Welcome.

Bill Kuhl

Friday, January 4, 2019

Electric Free Flight STRIX Timer #2

I have been having so much fun experimenting with electric free flights using the cheap STRIX motor timer and a 7 mm coreless motor. It will only run up to 10 seconds but that gives you a real good view of how the airplane is flying. You can really notice the slightest stall or if it is turning too tight. Making tiny adjustments to get the climb and glide paths just right can make a huge difference in the height of the climb and length of the glide.

This winter I finished a new plane for the electric combo a Sig Cub which looks to fly really well but I have been hesitant to make longer flights with it on the hard surfaces. Instead I have been flying a plane I made up from wing and tail of Flying Aces Moth, which is rather beat-up anyways. The wing is angled giving it too much stab tilt but I just do not seem to get around to fix it.

Sig Cub over Snow

The optimum size appears to be about 24" wingspan. Joshua Finn experimented with a plane using STRIX timer that appeared to be around that size. He even tried using the 8.5 mm motor used in E20 planes but found the battery was out of charge real fast. It would be fun to try a geared propeller too and see if the climb improves.

AMA Maxi Jr Electric

Dog Retrieved the Plane and this was the only Damage

One session flying the FA Moth type plane I had it in lift for a time and was happy it didn't fly any better. Recent flights have been from a frozen lake which gives a huge area to fly from but a crash into the bare ice would not be good. At some point I would like to design my own plane for the electric combo or maybe a couple planes with one using foam sheet.

The timer is now being sold for $5.99 https://www.banggood.com/STRIX-3_7V-1S-Free-Flight-Motor-Timer-For-6mm-7mm-Motor-p-1363923.html?akmClientCountry=America&cur_warehouse=CN 

Joshua Finn video on STRIX timer    https://youtu.be/kBThvOBYUzc 

First article

Bill Kuhl

I had much longer flights than this one but this is close.

Thursday, December 27, 2018

Thoughts on 2018 Looking to 2019

It has been an interesting year, mostly good but not completely, my mother passed away just before Thanksgiving but harder than that was seeing her suffer before it was all over. I enjoyed my hobbies when I could but found time to visit her every weekend and pushed her in the wheelchair either inside or outside the nursing home where she lived. I was so happy to see how nice the other residents were to her even though she seemed rather grumpy at times. It was strange to hear them tell me how proud she was of me, something she never told me which seems typical for her generation. 

New Gollywock Repaired

Sig Cub Electric Free Flight

Eureka E36 Climbing After Wing Recover

There is so much to do now as I pretty much left everything go but sure glad I did that. By the end of March I plan to have much more time when I retire. I am not counting the days as I enjoy my job and the people I work with, it is just there are things I rather do.  Now I realize that all the time can’t be spent building model airplanes as my house is pretty well full now. Related to the model aviation I would like to work more again with young people and the science projects.

Profile 1/2 A Control -line 2018 

This fall I repaired some of my free flight model airplanes and started building new ones. Simpler projects first like rocket gliders, sport electric free flight, and a catapult glider. For 2019 I have a good start on the construction of the BMJR Satellite GLH 320 ½ A gas free flight and ¼ A for TeeDee .020 Foo-2. I am also constructing a ½ A control line with built-up wing and fuselage the ½ A Viper.

Satellite 320 Wing Half

The other thing I want to expand in writing in the future is just how important science and engineering are to society. It seems emphasis is on athletics and arts but science and engineering is forgotten.

Bill Kuhl

Monday, December 3, 2018

Catching Up Almost Month Since Last Post

Outdoor flying in Minnesota has pretty much ended for me and I am trying to repair planes before building new ones for 2019. I have done some quicker builds between repairs; two rocket gliders, Science Olympiad catapult glider, and a Sig Cub setup for electric with STRIX timer. I did get one launch of Aleda R boost glider in the cold that went pretty well, just some stall in the glide. 

New Gollywock Fuselage Covered with Clear Mylar
Esaki Tissue Added

My mother passed away a couple of weeks ago and I have been busy with things related to her death. I did get the chance to give a science demo on electric motors, model solar cars, and model wind turbines. Made a visit to an after school class doing Science Olympiad and demonstrated my Protégé catapult glider. I hope to spend more time working with students and science related activities but I do not find much interest in that locally. 

Aleda R Boost Glider

Eureka E36 Short Test Flight

Reflecting on my free flight flying this year, I want to improve on my building and covering for next seasons models. I have been trying the tissue over mylar in more models and it is working better for me as I get the tissue attached without loose spots or wrinkles. On my Euerka e36 I recovered the wing with Polyspan lite which keeps the structure rigid in humid conditions but it is hard to fill the covering without using too much dope. I try to spot the places where tiny holes appear instead of so many coats on the whole structure. To get the stick joints closer to perfect in construction I ordered a Fourmost Miter Sander.

Sig Cub Electric

For several years I did not fly any model airplanes powered by a glow engine, only flew gliders or electric. At first I did not miss the mess or the noise but as I got into outdoor competition free flight I wanted to try glow engines again. Part of this was to be able to fly in more events, part has to do with nostalgia, and it is fun working with the engines. A friend even sent me a couple of model diesel engines which will be fun to get running. 

ED Hunter Diesel

Test Running Cox Medallion .049

In the back of mind I am thinking of attending a distant free flight contest this winter. Maybe not to fly or maybe fly an event that lends to easy airline travel.

Bill Kuhl

Related Links

Thursday, November 8, 2018

Importance of Materials in Model Aviation

After the end of the outdoor free flight contest season I have been reflecting on what I need to improve on for the future. I have also spent more time reading and watching videos on history and science. One aspect of my model building that I try to improve on is “materials”. In studying history, the most important discoveries that enabled new innovations, were the discovery of new materials. With the discovery of iron and later improving on this to create steel, so many things could be built or improved on as an example.

Witch Hawk 500 - Polyspan & Silkspan Covering

The model airplanes I most enjoy building are built primarily of balsa wood. Balsa is very strong for its weight and great to work with simple hand tools. It does vary in weight and hardness considerably and matching the proper density for the requirements needed in the model construction is critical to build a competitive free flight model. Not paying enough attention to this I have built models that were too heavy or were not strong enough in critical places and broke just from flight loads. Not only is the density of balsa important but also the grain types created by how the balsa was cut from the balsa logs.

1/2 A Streak Wing Does Not Sag with Polyspan Lite

Another part of the model construction I have been trying to refine is the proper covering material for the type of model I am building. In the past I most often used a plastic iron-on covering when possible, for smaller models it was tissue paper. For the past couple of years I have had a fascination with the older free flight models. With the older designs the structure was lacking the rigidity needed without using a covering material that gave the structure the strength needed. Yet another aspect of the covering selection that became apparent with the past flying season was what humidity did to the covering. Esaki tissue which is really the only choice for many smaller models starts to sag terribly in early morning or late evening when I often fly. Besides taking on extra weight now that the covering is no longer tight on the model, the structure becomes less rigid.

Wilbur Center Section Repaired with Tissue over Mylar

Last winter in my building I tried covering with Polyspan and using mylar under the Esaki tissue. Polyspan does not change with water; to shrink it heat is used. It only comes in white and needs to be filled with nitrate dope before applying the color. I had purchased airbrush equipment and this worked well for finishing the Polyspan. There is also a Polyspan Lite which is considerably lighter but harder to fill. I used this on smaller gas models; it did stay tight but will puncture easily. 

New Gollywock Tissue over Mylar

Many people recommend covering models with ¼ mylar and then covering over this with tissue. It sounded like a lot of work but I did try it on a New Gollywock model I was building. On the first model I believe I did not get the tissue attached properly resulting in loose spots and wrinkles. In doing a repair on center section of Wilbur rubber model I did a better job of sealing the tissue to the mylar. The covering does not sag in humid conditions but the tissue will still take on weight from the water.

Eureka e36 Wing Recover with Polyspan Lite - Sagging Tissue on Stab

For me the challenges of getting the choices closer to optimum in building an outdoor free flight model is what makes it so fun. No doubt with more experience I will become more uniform on the choices of wood and covering material. What I appreciate with the rules for the classes of free flight models I fly is that I am forced to do this and cannot just buy a high-tech composite model that was constructed in molds.

Bill Kuhl

Friday, November 2, 2018

Free Flight Fun Projects & Repairs

After the outdoor free flight contest season has finished I have been busy repairing planes and trying some quick new planes. In a previous post I had mentioned working with the STRIX electric timer and flying on a direct drive 7 mm motor. Last weekend I had some good flights using this setup in an AMA Maxi Jr rubber model converted to electric. As I got the turn circle dialed in the flights became higher lasting about 35 seconds on the 10 second power run. The last flight ended when a dog grabbed the plane by the wing and started to carry it back. Only the tissue was ripped. I have to believe with a lighter plane a minute flight is possible, which would be about perfect for a small flying site.

NJAPF Fuselage Repaired 

Only Damage After Carried by Dog

AMA Maxi Jr Electric

At the last outdoor Minnesota contest I flew my NJAPF p30 and the DT line broke, after the contest I decided it was time to recover the fuselage that had numerous patches. What surprised me a little was there were broken glue joints that the covering had hidden. After repairing the structure and twisting it to check for more questionable joints, I did find more. My plan is to replace the viscous stab DT system with a wing pop off using a fuse.

Eureka E36 Test Flight after Repairs

After a crash at the Nats I finished repairs on my Eureka e36 NOS. The wing was recovered with Polyspan Lite because I did not like the sagging tissue in humid conditions. My repair in one spar in the wing was not adequate as it broke again on the first low level DT landing. This has been repaired and more short flights went well. 

FAC Tic Catapult Gliders

G12 Catapult Glider

A couple of simple catapult gliders were finished the first being the FAC Tic from Easybuilt which comes in a 2-pack. The first one I messed up in that I did not get the dihedral blocked up well when using Testors glue, trying to fix this I did not do the best job either. The second one I used CA and got everything aligned. This glider flies really well for only having a 6” wingspan. I also finished up a second G12 Catapult glider with the flapped trailing edge. Richard Bertrand uses this glider in his Free Flight Rescue program for kids. The glider is stable and can handle a full stretch launch with ¼” rubber.

Aleda R Boost Glider
Switchblade S Wing Forward

Wing Back

  For something different I have built two rocket glider kits purchased from J&H Aerospace. One is a boost glider where the motor tube and nose cone separate from a glider. The other is a swing wing glider that has the wing halves move forward when the ejection charge releases the tension on two lines holding the wing halves swept back 90 degrees. This should be fun to see go up.

I have a new fuselage to build for a New Gollywock and then plan to start building some new models.

Bill Kuhl

Related Links

https://jhaerospace.com/product/aleda-r-boost-glider/  Aleda R Boost Glider
https://jhaerospace.com/product/switchblade-s-rocket-glider-kit/  Switchblade S Rocket Glider
https://easybuiltmodels.com/g09.htm Easy Built FAC Tic catapult glider